Newborns who weigh around 9 pounds or more at birth tend to have bigger brains as teens than those who weigh less at birth, a new study finds. Although the differences in brain size may affect brain development in childhood, the full scope of those effects still isn't known, the researchers added. "It has been well known for some time that premature birth and very low birth weight can affect brain development," said study author Kristine Beate Walhovd, a professor of neuropsychology at the University of Oslo in Norway. "This study shows that also normal variation in birth weight is predictive of brain characteristics many years later."